Phase-contrast (PC) magnetic resonance imaging (“MRI”) is an established technique for measuring blood velocities in vivo and is in wide clinical use. Conventional PC-MRI is based on spoiled gradient recalled echo (“GRE”) pulse sequences, which provide consistent image quality. PC MRI techniques have been developed that are based on balanced steady state free precession (SSFP) sequences, which provide accurate velocity measurements with superior signal to noise ratio (“SNR”) efficiency.
Rapid imaging sequences or steady-state free precession (abbreviated, “SSFP”) sequences acquire imaging data in a dynamic equilibrium state (i.e., the so called “steady-state”). Due to the heavy requirements on system performance, these types of SSFP sequences were not in use until recently. Presently, such imaging sequences have become increasingly popular due to their very fast scanning properties, which are necessary for imaging fast dynamic processes, in abdominal imaging, in cardiac imaging, or when imaging very ill and traumatized patients. There are many different types of steady-state imaging sequences, and a special member of this group is obtained if the time integral of each of the three gradients is zero—e.g. “balanced”—within each repetition time (TR). Such a pulse sequence is disclosed, for example, as FIG. 3 in U.S. Pat. No. 4,769,603, the entire contents of which are incorporated herein by reference.
Such approaches typically involve the acquisition of two or more complete datasets, where at least one serves as a phase reference. The requirement for acquiring multiple datasets limits the spatio-temporal resolution obtainable within a given total imaging time, and impedes real-time imaging. In addition, the acquisition of multiple datasets can present inconveniences and discomfort for MRI subjects.